Lesson 20: TCP/IP Layer Structure Deep Dive

Let’s examine the specific roles and protocols within the four TCP/IP layers.

1. Network Access Layer (OSI L1 & L2)

• Role: Defines how to physically connect to the network medium and the protocols needed to manage data exchange within the local network segment.
• Protocols: Ethernet, Wi-Fi, ARP, and various physical signaling standards.

2. Internet Layer (OSI L3)

• Role: Providing logical addressing and routing across internetworks. This layer is responsible for selecting the best path for data to travel.
• Protocols: IP (Internet Protocol) is the defining protocol. Others include ICMP (Internet Control Message Protocol) and IGMP (Internet Group Management Protocol).

3. Transport Layer (OSI L4)

• Role: Provides communication services for the Application Layer. It manages reliable (or unreliable) end-to-end data delivery and uses port numbers to direct traffic to the correct application.
• Protocols: TCP (Transmission Control Protocol) and UDP (User Datagram Protocol).

4. Application Layer (OSI L5, L6, L7)

• Role: Houses the protocols that communicate directly with end-user applications, providing formatting, session management, and specific service delivery.
• Protocols: DNS, HTTP/HTTPS, FTP, SMTP, SSH.

Memorization Tip: The critical protocols, IP (Internet Layer) and TCP/UDP (Transport Layer), give the model its name.